diff --git a/04_potentiel_electrique.md b/04_potentiel_electrique.md
index 2f56a2c3bd9337dbe3e3d1995e919be231834388..e8f0e9f7bf59d07193b96d1284db8755e4cac054 100644
--- a/04_potentiel_electrique.md
+++ b/04_potentiel_electrique.md
@@ -395,7 +395,7 @@ Les capacités sont représentées dans des circuits électriques pas un symbole
comme si la @fig:cap_symbol
{#fig:cap_symbol width=50%}
+électrique.](figs/cap_symbol.svg){#fig:cap_symbol width=20%}
Si on applique un voltage (un potentiel), $V$, entre les deux plaques en les
connectant à une batterie ou à une prise électrique par exemple, une des deux
diff --git a/06_cicruits_electriques.md b/06_cicruits_electriques.md
index 8bcc3b007985a15828e03050a8fb9fa610c39f66..432906d9f8b78359aa4d07b854edbb242f12e690 100644
--- a/06_cicruits_electriques.md
+++ b/06_cicruits_electriques.md
@@ -216,10 +216,42 @@ Considérons maintenant le cas de capacités en série (voir @fig:three_cap).
---
-Exercice (Capacité équivalente) #
+Question (Capacité équivalente) #
Déterminer la capacité équivalente des capacités branchées en série.
Indication: Il faut évaluer $V$ en fonction des chutes de potentiel.
---
+
+
+---
+
+Solution (Capacité équivalente) #
+
+Le voltage total au travers de toutes les capacités doit être donné par la somme des voltages au travers de chaque capacité
+$$
+V=V_1+V_2+V_3.
+$${#eq:tot_volt}
+On sait aussi que le charge est la même sur chaque capacité (conservation de la charge) et donc
+$$
+Q=C_1V_1=C_2V_2=C_3V_3.
+$$
+On peut réécrire @eq:tot_volt comme
+$$
+\frac{Q}{C_\mathrm{eq}}=\frac{Q}{C_1}+\frac{Q}{C_2}+\frac{Q}{C_3}=Q\left(\frac{1}{C_1}+\frac{1}{C_2}+\frac{1}{C_3}\right).
+$$
+
+---
+
+## Les circuits RC
+
+Souvent les capacités et résistances sont connectées en série dans les circuits électriques (voir @fig:rc). C'est même un composant essentiel
+dans quasiment tous les circuits du monde.
+Ces circuits sont particulièrement utiles quand
+les courant n'est pas stationnaire (qu'il dépend du temps). Dans cette section on va analyser les circuits RC dans certains cas particuliers.
+
+{#fig:rc width=50%}
+
+
+
diff --git a/figs/rc.svg b/figs/rc.svg
new file mode 100644
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--- /dev/null
+++ b/figs/rc.svg
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